The N-phosphonomethyl-glycines, of which glyphosate is a member, have proven to be an extremely valuable herbicides. Their soluble salts have been incorporated into various formulations which are extremely effective in controlling various plants and weeds that are detrimental to the growth and development of various cash crops and agricultural plants. N-phosphonomethyl-glycine can thus kill or inhibit the growth, reproduction, or proliferation of various weeds, which left untreated, would destroy or diminish the growth of crops, fruit trees, and other valuable plants.
Franz, U.S. Pat. No. 3,799,758, relates to N-phosphonomethylglycine and its derivatives which are useful as herbicides. This reference provides guidance into the preparation of various compounds which comprise the N-phosphonomethylglycine family.
Two other Franz references, U.S. Pat. Nos. 3,977,860 and 4,405,531, respectively, relate to salts of N-phosphonomethylglycine and to herbicidal compositions utilizing the esters of N-phosphonomethylglycine. The '531 patent, in particular, discloses the use of isopropyl amine salt of N-phosphonomethylglycine. This product is available from Monsanto Company of St. Louis, Mo. under the trademark ROUNDUP.RTM..
Other insights into the art may be gleaned from a review of Moller, U.S. Pat. No. 5,118,338 and Darchy et al., U.S. Pat. No. 5,180,414. These references also relate to herbicidal compositions containing one or more salts of N-phosphonomethylglycine.
Unfortunately, N-phosphonomethyl-glycine is not particularly selective in its application as a herbicide. In many instances, it can kill or reduce the incidence of the "good" plants and crops, along with the weeds and other undesirable vegetation. Soybeans in particular have shown themselves to be especially vulnerable to the toxicity of N-phosphonomethyl-glycine and its salts. Data exists which show that a major percentage of a soybean crop can be damaged or lost upon each application of this herbicide. In typical applications of about 0.5 to 1.0 lbs/acre of N-phosphonomethyl-glycine, as much as 25-50% of the soybean plants will exhibit some form of visible injury. In some applications, this figure can be as high as 80%.
There thus exists a need in the art to develop effective herbicidal formulations containing N-phosphonomethylglycines which show greater selectivity in removing or controlling weeds, while minimally affecting valuable agricultural crops.
Acifluorfen is another valuable herbicide which has demonstrated toxic efficacy against a wide array of weeds. Acifluorfen is derived from the family of certain diphenylethers. Various salts of acifluorfen are available from BASF Corporation under the trademark BLAZER.RTM.. More specifically, Bayer et al., U.S. Pat. No. 4,063,929 (U.S. Pat. No. RE 31,455) is directed to herbicidal 4-trifluoromethyl-4-nitrodiphenyl ethers and the numerous salts thereof, and is incorporated herein by reference. The '929 patent lists the preparation and uses of various diphenyl ethers in herbicidal applications.
Combinations of N-phosphonomethylglycines and acifluorfen derivatives are known in the art as herbicides. For example, WO 84/03607, assigned to the Chevron Research Company, describes a glyphosate-type herbicidal composition with a minor amount of an acifluorfen type herbicide. The compositions reportedly exhibit an increased speed of phytotoxic action when compared with glyphosates alone.
Borrod et al., U.S. Pat. No. 5,147,444, also relates to a combination of glyphosate and acifluorfen for use as a herbicide. The patentees describe advantages of the combination as including increased speed of action, and improved activity. In addition, EP A 284,419 is directed to herbicides containing both acifluorfen and glyphosate.
It is unfortunate that none of the cited references appear to address the issue of how to avoid destroying or damaging valuable cash crops and other desirable vegetation by the use of the combination of the N-phosphonomethyl-glycines with acifluorfen.
It has now been discovered that a certain quantity of either herbicide together in combination exhibits what as been described as a "safening" effect. This means that when N-phosphonomethyl-glycine and acifluorfen are applied to crops, and especially soybeans, the incidence of damage to the crops is greatly reduced, as compared with similar applications of just the highly toxic N-phosphonomethyl-glycine alone. At the same time, the combination remains efficacious in reducing or eliminating undesirable weeds and other vegetation which is destructive to the crops.